A digital standard definition-video cassette recorder (SD-VCR) that is capable of recording and reproducing ATV signals on digital video tapes is currently being developed for consumer use. Furthermore, the SD-VCR is able to transmit data at 24.9 Mbits per second, and the ATV signal which is recorded or reproduced from the SD-VCR has a transmission rate of 19.3 Mbits per second. Consequently, the SD-VCR is capable of recording or reproducing additional data to and from the video tape at a rate of 5.6 Mbits per second.
In order to more fully utilize the unused area of the video tape, various methods are currently being tested in which trick play data is recorded in the unused area so that the ATV signal can be reproduced during a trick play mode (e.g. a high speed forward reproduction mode, a high speed reverse reproduction mode, or any other non-normal speed reproduction mode). Furthermore, developing an efficient process for recording and reproducing such trick play data is essential for enabling various types of scanners (i.e. video heads) to reproduce signals at a variety of speeds during the trick play mode. Furthermore, such method will also improve the image quality of video signals and remove noise from the video signals.
In order to provide a better understanding of the present invention, the composition of an ATV signal will be briefly described below in conjunction with FIG. 1. As shown in the figure, the ATV signal contains a transport bit stream which includes a series of groups-of-pictures (GOPs), and each GOP has a certain number of pictures (e.g. 12 pictures) arranged in a particular order. The various pictures contained in the GOP may include intra-coded pictures (I-pictures), predictive-coded pictures (P-pictures), and bidirectionally predictive-coded pictures (B-pictures).
The I-pictures are digitally represented by the greatest number of bits and have the most significant effect upon the image quality of the entire GOP and the capability of encoding the various P-pictures. Since the I-pictures, or intra-frames, contain a large number of bits, they can be independently coded and decoded.
The P-pictures are represented by fewer bits than the I-pictures and are coded or decoded based on the information contained in the various I-pictures. Specifically, the P-pictures are predicted frames which are encoded by compensating for the movement contained in the previous intra-frames or the previous predicted frames.
The B-pictures are represented by a smaller number of bits than the P-pictures and are coded or decoded in accordance with the information contained in the various I-pictures and P-pictures. In particular, the B-pictures are bidirectionally predicted frames which are encoded by compensating for the movement contained in the previous intra-frames, subsequent intra-frames, previous predicted frames, and/or subsequent predicted frames.
When all of the I-pictures, P-pictures, and B-pictures are encoded, they are arranged in a predetermined order to form the GOP. For instance, as illustrated in FIG. 1, the pictures are organized in the following order: I-B-B-P-B-B-P-B-B-P-B-B-I.
Each of the pictures are further divided into various segments. Specifically, each picture contains a certain number of slices, and each slice includes a predetermined number of macro blocks. In addition, each macro block comprises a number of discrete cosine transform (DCT) blocks.
Conventional apparatuses cannot appropriately record and reproduce normal video data and trick play data when the ATV signal is recorded or reproduced in accordance with a Moving Picture Expert Group (MPEG)-2 format. For example, when the ATV signal is recorded, the P-pictures and B-pictures can only be decoded after the I-pictures have been completely decoded. As a result, decoding the P-pictures and B-pictures and reproducing the ATV signal at a high-speed is impossible.